1. Field of the Invention
The present invention relates to a wafer holder having exceptional rigidity and heating uniformity, and in particular relates to a wafer holder and a heater unit used in a wafer prober for mounting a semiconductor wafer on a wafer-mounting surface and pressing a probe card against the wafer to inspect the electrical characteristics of the water, and to a wafer prober on which the wafer holder and the heater are mounted.
2. Description of the Background Art
In the prior art, a heating procedure is performed in a semiconductor inspection step on a semiconductor substrate (wafer) to be treated. Specifically, the wafer is heated to a temperature higher than the normal operating temperature, potentially defective semiconductor chips are made to fail at an accelerated rate and are removed, and a burn-in is performed to prevent the occurrence of defects after shipping. In the burn-in step, after the semiconductor circuits are formed on the semiconductor wafer and before the wafer is diced into individual chips, the electrical characteristics of each chip are measured while heating the wafer, and defective chips are removed. A strong demand has existed for the processing time to be reduced in the burn-in step in order to improve throughput.
In such a burn-in step, the semiconductor substrate is supported and heated using a heater. Since the entire reverse surface of the wafer must be in contact with a ground electrode, conventional heaters have been made of metal. A wafer on which circuits are formed is mounted on a metal flat plate heater, and the electrical characteristics of the chips are measured. A measuring instrument called a probe card, which is provided with numerous electrically conducting electrode pins, is pressed onto the wafer with a force of tens to hundreds of kilograms-force when the measurements are made. Therefore, if the heater is thin, the heater may be deformed, causing gaps to form between the wafer and the probe pins, and contact failure to occur. Therefore, the use of thick metal plates having a thickness of 15 mm or greater has been necessary in order to preserve rigidity such that the heater is not deformed. The heat capacity of the heater therefore becomes relatively large, and long periods are required for raising and lowering the temperature of the heater, which has become a large obstacle to improving throughput.
Additionally, in the burn-in step, electricity is applied to the chips, and the electrical characteristics are measured. However, with the increasing power output of chips in recent years, the chips generate large amounts of heat when the electrical characteristics are measured, and are sometimes damaged by the heat they generate. Rapid cooling after measurement has therefore been needed. Additionally, heating needs to be as uniform as possible during measurement. Copper (Cu), which has a high thermal conductivity of 403 W/mK, has therefore been used as the metal material.
Accordingly, in Japanese Laid-Open Patent Application Publication No. 2001-033484, a wafer prober is proposed wherein a thin metal layer and not a thick metal plate is formed on the surface of a thin but highly rigid ceramic substrate, resulting in minimized deformation and a low heat capacity. Since this wafer prober has high rigidity, contact failures do not occur. Since this wafer prober has low heat capacity, the temperature can be raised and lowered in a short time. Also disclosed is the use of an aluminum alloy, stainless steel or the like for the support member used to position the wafer prober.
However, if, as disclosed in Japanese Laid-Open Patent Application Publication No. 2001-033484, the wafer prober is only supported at the outermost periphery, the wafer prober may bend due to the pressure of the probe card. Therefore, measures such as providing a large number of support pillars or the like have been necessary.
Furthermore, with the scale of the semiconductor process decreasing over the past several years, a demand has arisen for increased load per unit area during probing and for precise alignment between the probe card and prober. The prober usually repeatedly performs an operation in which the wafer is heated to a predetermined temperature, and moved to a predetermined position during probing, whereupon a probe card is pressed on the wafer. In this case, high precision is also required in the drive system in order to move the prober to the predetermined position.
However, when the wafer is heated to a prescribed temperature; i.e., to about 100° C. to about 200° C., the heat is conveyed to the drive system, and problems have arisen in regard to a loss of precision due to thermal expansion of the metal components of the drive system. Furthermore, due to the increased load during probing, the wafer-holding prober itself must be rigid. Specifically, problems have been presented in that, if the wafer prober itself deforms under load during probing, the pins of the probe card will not be able to make uniform contact with the wafer, thereby rendering inspection impossible, or, in the worst case, damaging the wafer. For this reason, probers are made larger in order to inhibit deformation, and problems have arisen in that the weight of the prober increases and the increased weight affects the precision of the drive system. A problem also arises in that as the size of the prober increases, much more time is required to increase or reduce the temperature of the prober, and throughput decreases.
In order to improve throughput, cooling mechanisms are often provided to improve the heating and cooling rate of the prober. Conventionally, however, cooling mechanisms have employed air cooling, as in Japanese Laid-Open Patent Application Publication No. 2001-033484, for example, or envisaged the provision of a cooling plate directly below the metal heater. Problems have arisen in the former case in that the cooling rate of air cooling is low. Problems have also arisen in the latter case in that deformations in the metal cooling plate occur easily during probing due to the direct pressure applied to the cooling plate by the probe card.
In semiconductor production, heater units for heating semiconductor substrates and the like are used in order to heat and dry a resist solution applied to the substrate in the lithography step, for example. Efforts are being made to reduce the cost of products obtained by mass production based on continuous operation in such semiconductor manufacturing. Therefore, manufacturing apparatuses that will shorten the cycle time are desired. In order to obtain high throughput for a single apparatus, reductions are necessary not only in the processing time during periods when the temperature of the materials to be treated is maintained, but in the time necessary to change the heating temperature in accordance with changes in the processing conditions (heating time and cooling time). The temperature of the heater plate and the article to be treated, which is mounted on the heater plate, can be lowered in a short time by bringing cooling blocks having the desired heat capacity into contact with the heated heater plate, as in Japanese Laid-Open Patent Application Publication No. 2004-014655. The result is that a decrease in the time necessary for the heat treatment step is proposed. However, due to the existence of a boundary surface between the cooling blocks and the heater, problems have arisen in this invention in that contact resistance occurs and the cooling rate cannot be increased beyond a certain level.